It is known that a rotary tablet press has pairs of upper and lower rams arranged around a rotatable mould table, and all the upper rams and all the lower rams are secured in an airtight manner to respective flexible annular intermediate walls which cover the ram shanks. These intermediate walls are secured in an airtight manner at least with its inner edge to the mould table and situated between the mould table and the upper ram guides or lower ram guides respectively.
In order to keep away from the ram shanks the mouldable material powder or dust which whirls about during the operation of the rotary tablet presses, it is known (DE-PS 30 49 597) to arrange between the mould shelf and the ram guides in the mould table an annular sealing wall which is secured with its edges on the mould table and has holes arranged in a circle in which the ram shanks sit. As a result only the moulding heads of the rams, which heads enter into the moulds, are in the dust-filled region above and below the mould shelf, whereas the ram shanks, moving upwards and downwards in their slide guides in the mould table, are shielded by the flexible walls and substantially protected from the access of dust.
But when that known press is in operation it has been found that it is not possible to achieve complete protection of the ram shanks against dust, which shanks are covered with a lubricant film, since, as the rams move rotationally, they carry out different up and down movements from one another, and as a result there is non-uniform deformation of the intermediate walls in which the ram shanks are situated and to which they are secured. Especially the intermediate walls are subjected to very strong dragging forces in the region between the rams, which succeed one another in close succession in the circumferential direction of the mould table, and undergo considerable stress, because the spacing between neighbouring rams in the region of their fastening zones is changed during the moulding operation when these fastening zones of neighbouring rams get into different height positions. These rapidly recurring dragging forces in the circumferential direction quickly lead to fatigue of the elastomer of which the intermediate walls are made, and cause cracks in the intermediate wall. The ram shanks are then no longer securely arranged in the holes associated with them in the intermediate wall, and instead become pulled out of the latter, and the intermediate wall tears at the same time and becomes unusable.